A polarizing plate is an apparatus configured to convert natural light into polarized light having a certain vibration direction. In recent years, polarizing plates have been applied to various display devices such as Liquid Crystal Display (LCD) devices, Organic Light Emitting Diode (OLED) devices, and the like.
Such a polarizing plate is generally used in a structure in which a protective film is attached to one or both surfaces of a polarizer via an adhesive, wherein the polarizer is formed using a polyvinyl alcohol (PVA)-based resin stained with a dichroic dye or iodine. According to the related art, triacetyl cellulose (TAC)-based films have been widely used as protective films configured to protect such a polarizing plate. However, such TAC films have problems in that such films may be easily deformed under conditions of high temperature and high humidity. Therefore, protective films formed using various materials, able to be substituted for such TAC films, are currently in development. For example, alternative methods of forming such protective films using polyethylene terephthalate (PET), cycloolefin polymer (COP), acrylic film, and the like, alone or in combination, have been proposed.
Meanwhile, an aqueous adhesive composed of an aqueous solution of a polyvinyl alcohol-based resin has been generally used as an adhesive with which to attach such a protective film to a polarizer.
However, such an aqueous adhesive may have a problem in that the use thereof is limited according to a material of a film, since this aqueous adhesive has weak adhesive strength when an acrylic film or a COP film is used instead of using the TAC film as the protective film. Also, this aqueous adhesive has problems in that when the protective films applied to both surfaces of a PVA element are formed using different materials, curling may occur in edge portions of the polarizing plate in a process of drying the aqueous adhesive, and initial optical properties may be deteriorated in addition to poor adhesive strength resulting from different types of materials being used in films. Accordingly, a non-aqueous photocurable adhesive was proposed as an alternative to solve the above-listed problems.
However, in the case of the related art, when such a non-aqueous photocurable adhesive is applied to a double-sided polarizing plate in which protective films are attached to both surfaces of the polarizer, adhesive layers formed on both surfaces of the polarizer should be respectively cured, leading to difficulties in processes in which a light irradiation process needs to be performed twice.
Meanwhile, to simplify a manufacturing process, when the adhesive layers formed on both surfaces of the polarizer are cured through a single light irradiation process, degrees of curing of the adhesive layers may be different, due to a difference in amounts of light reaching a light-irradiated surface and a non-light irradiated surface, resulting in deteriorated adhesive strength and peel strength of the non-light irradiated surface. When the adhesive strength of the adhesive layers is deteriorated, durability of the polarizing plate may be degraded, leading to deteriorations in optical physical properties and reworkability.